Mesenchymal/epithelial regulation of retinoic acid signaling in the olfactory placode

We asked whether mesenchymal/epithelial (M/E) interactions regulate retinoic acid (RA) signaling in the olfactory placode and whether this regulation is similar to that at other sites of induction, including the limbs, branchial arches, and heart. RA is produced by the mesenchyme at all sites, and subsets of mesenchymal cells express the RA synthetic enzyme RALDH2, independent of M/E interactions. In the placode, RA-producing mesenchyme is further distinguished by its coincidence with a molecularly distinct population of neural crest-associated cells. At all sites, expression of additional RA signaling molecules ( CRABP1) depends on M/E interactions. Of these molecules, RA regulates only , and this regulation depends on M/E interaction. Expression of and all of which are thought to influence RA signaling, is also regulated by M/E interactions independent of RA at all sites. Despite these common features, expression is distinct in the placode, as is regulation of and RALDH2 by Fgf8. Thus, M/E interactions regulate expression of RA receptors and cofactors in the olfactory placode and other inductive sites. Some aspects of regulation in the placode are distinct, perhaps reflecting unique roles for additional local signals in neuronal differentiation in the developing olfactory pathway

Mesenchymal/epithelial regulation of retinoic acid signaling in the olfactory placode

We asked whether mesenchymal/epithelial (M/E) interactions regulate retinoic acid (RA) signaling in the olfactory placode and whether this regulation is similar to that at other sites of induction, including the limbs, branchial arches, and heart. RA is produced by the mesenchyme at all sites, and subsets of mesenchymal cells express the RA synthetic enzyme RALDH2, independent of M/E interactions. In the placode, RA-producing mesenchyme is further distinguished by its coincidence with a molecularly distinct population of neural crest-associated cells. At all sites, expression of additional RA signaling molecules ( CRABP1) depends on M/E interactions. Of these molecules, RA regulates only , and this regulation depends on M/E interaction. Expression of and all of which are thought to influence RA signaling, is also regulated by M/E interactions independent of RA at all sites. Despite these common features, expression is distinct in the placode, as is regulation of and RALDH2 by Fgf8. Thus, M/E interactions regulate expression of RA receptors and cofactors in the olfactory placode and other inductive sites. Some aspects of regulation in the placode are distinct, perhaps reflecting unique roles for additional local signals in neuronal differentiation in the developing olfactory pathway

Molecular Specification and Patterning of Progenitor Cells in the Lateral and Medial Ganglionic Eminences

We characterized intrinsic and extrinsic specification of progenitors in the lateral and medial ganglionic eminences (LGE and MGE). We identified seven genes whose expression is enriched or restricted in either the LGE: Boc, Fzd8, Ankrd43 and Ikzf1, or MGE: Mbip, Zswim5, and Adamts5. Boc, Fzd8, Mbip and Zswim5 are apparently expressed in LGE or MGE progenitors, while the remaining three are seen in the post-mitotic mantle zone. Relative expression levels are altered and regional distinctions are lost for each gene in LGE or MGE cells propagated as neurospheres; indicating that these newly identified molecular characteristics of LGE or MGE progenitors depend upon forebrain signals not available in the neurosphere assay. Analyses of Pax6Sey/Sey, Shh−/−, and Gli3XtJ/XtJ mutants suggests that LGE and MGE progenitor identity does not rely exclusively upon previously established forebrain-intrinsic patterning mechanisms. Among a limited number of additional potential patterning mechanisms, we found that extrinsic signals from the frontonasal mesenchyme are essential for Shh and Fgf8-dependent regulation of LGE and MGE genes. Thus, extrinsic and intrinsic forebrain patterning mechanisms cooperate to establish LGE and MGE progenitor identity, and presumably their capacities to generate distinct classes of neuronal progeny

Specific Mesenchymal/Epithelial Induction of Olfactory Receptor, Vomeronasal, and Gonadotropin-Releasing Hormone (GnRH) Neurons

We asked whether specific mesenchymal/epithelial (M/E) induction generates olfactory receptor neurons (ORNs), vomeronasal neurons (VRNs), and gonadotropin-releasing hormone (GnRH) neurons, the major neuron classes associated with the olfactory epithelium (OE). To assess specificity of M/E-mediated neurogenesis, we compared the influence of frontonasal mesenchyme on frontonasal epithelium, which becomes the OE, with that of the forelimb bud. Despite differences in position, morphogenetic and cytogenic capacity, both mesenchymal tissues support neurogenesis, expression of several signaling molecules and neurogenic transcription factors in the frontonasal epithelium. Only frontonasal mesenchyme, however, supports OE-specific patterning and activity of a subset of signals and factors associated with OE differentiation. Moreover, only appropriate pairing of frontonasal epithelial and mesenchymal partners yields ORNs, VRNs, and GnRH neurons. Accordingly, the position and molecular identity of specialized frontonasal epithelia and mesenchyme early in gestation and subsequent inductive interactions specify the genesis and differentiation of peripheral chemosensory and neuroendocrine neurons.Molecular and Cellular Biolog

22q11 Gene dosage establishes an adaptive range for sonic hedgehog and retinoic acid signaling during early development

We asked whether key morphogenetic signaling pathways interact with 22q11 gene dosage to modulate the severity of cranial or cardiac anomalies in DiGeorge/22q1 deletion syndrome (22q11DS). Sonic hedgehog (Shh) and retinoic acid (RA) signaling is altered in the brain and heart—clinically significant 22q11DS phenotypic sites—in LgDel mouse embryos, an established 22q11DS model. LgDel embryos treated with cyclopamine, an Shh inhibitor, or carrying mutations in Gli3Xtj, an Shh-signaling effector, have morphogenetic anomalies that are either not seen, or seen at significantly lower frequencies in control or single-mutant embryos. Similarly, RA exposure or genetic loss of RA function via heterozygous mutation of the RA synthetic enzyme Raldh2 induces novel cranial anomalies and enhances cardiovascular phenotypes in LgDel but not other genotypes. These changes are not seen in heterozygous Tbx1 mutant embryos—a 22q11 gene thought to explain much of 22q11DS pathogenesis—in which Shh or RA signaling has been similarly modified. Our results suggest that full dosage of 22q11 genes beyond Tbx1 establish an adaptive range for morphogenetic signaling via Shh and RA. When this adaptive range is constricted by diminished dosage of 22q11 genes, embryos are sensitized to otherwise benign changes in Shh and RA signaling. Such sensitization, in the face of environmental or genetic factors that modify Shh or RA signaling, may explain variability in 22q11DS morphogenetic phenotypes

Workshop to identify critical windows of exposure for children's health: neurobehavioral work group summary.

This paper summarizes the deliberations of a work group charged with addressing specific questions relevant to risk estimation in developmental neurotoxicology. We focused on eight questions. a) Does it make sense to think about discrete windows of vulnerability in the development of the nervous system? If it does, which time periods are of greatest importance? b) Are there cascades of developmental disorders in the nervous system? For example, are there critical points that determine the course of development that can lead to differences in vulnerabilities at later times? c) Can information on critical windows suggest the most susceptible subgroups of children (i.e., age groups, socioeconomic status, geographic areas, race, etc.)? d) What are the gaps in existing data for the nervous system or end points of exposure to it? e) What are the best ways to examine exposure-response relationships and estimate exposures in vulnerable life stages? f) What other exposures that affect development at certain ages may interact with exposures of concern? g) How well do laboratory animal data predict human response? h) How can all of this information be used to improve risk assessment and public health (risk management)? In addressing these questions, we provide a brief overview of brain development from conception through adolescence and emphasize vulnerability to toxic insult throughout this period. Methodological issues focus on major variables that influence exposure or its detection through disruptions of behavior, neuroanatomy, or neurochemical end points. Supportive evidence from studies of major neurotoxicants is provided

Mitochondrial localization and function of a subset of 22q11 deletion syndrome candidate genes

Six genes in the 1.5 MB region of chromosome 22 deleted in DiGeorge/22q11 Deletion Syndrome—Mrpl40, Prodh, Slc25a1, Txnrd2, T10, and Zdhhc8—encode mitochondrial proteins. All six genes are expressed in the brain, and maximal expression coincides with peak forebrain synaptogenesis shortly after birth. Furthermore, their protein products are associated with brain mitochondria, including those in synaptic terminals. Among the six, only Zddhc8 influences mitochondria-regulated apoptosis when overexpressed, and appears to interact biochemically with established mitochondrial proteins. Zdhhc8 has an apparent interaction with Uqcrc1, a component of mitochondrial complex III. The two proteins are coincidently expressed in presynaptic processes; however, Zdhhc8 is more frequently seen in glutamatergic terminals. 22q11 deletion may alter metabolic properties of cortical mitochondria during early post-natal life, since expression complex III components, including Uqcrc1, is significantly increased at birth in a mouse model of 22q11 deletion, and declines to normal values in adulthood. Our results suggest that altered dosage of one, or several 22q11 mitochondrial genes, particularly during early postnatal cortical development, may disrupt neuronal metabolism or synaptic signaling

Myocardial injury revealed by plasma troponin I in breast cancer treated with high-dose chemotherapy

Background: High-dose chemotherapy (HDC) has been widely utilized in high-risk breast cancer, but it may induce cardiac toxicity. Cardiac dysfunction may become evident weeks or months after HDC and, to date, no early markers of myocardial injury that are able to predict late ventricular impairment are available. We investigated the role of plasma troponin I (TnI) in this setting. Patients and methods: We measured TnI plasma concentration after HDC in 211 high-risk breast cancer women (46 \ub1 11 years, mean \ub1 SD). According to TnI value (<0.5 or 650.5 ng/ml), patients were allocated into a troponin positive (TnI+; n = 70) and a troponin negative (TnI-; n = 141) group. All patients underwent left ventricular ejection fraction (LVEF, Echo) examination during the following 12 months. Results: LVEF progressively decreased in the TnI+ group but not in the TnI- group. In TnI+ patients a close relationship between the TnI increase, as well as the number of positive TnI assays, and the maximal LVEF decrement, was found (r = 0.92, P <0.0001 and r = 0.93, P < 0.0001, respectively). Conclusions: In our population, the elevation of TnI soon after HDC accurately predicts the development of future LVEF depression. In this setting, TnI can be considered a sensitive and reliable marker of myocardial damage with relevant clinical and prognostic implications

Developmental regulation of neural cell adhesion molecule in human prefrontal cortex

Neural cell adhesion molecule (NCAM) is a membrane-bound cell recognition molecule that exerts important functions in normal neurodevelopment including cell migration, neurite outgrowth, axon fasciculation, and synaptic plasticity. Alternative splicing of NCAM mRNA generates three main protein isoforms: NCAM-180, -140, and -120. Ectodomain shedding of NCAM isoforms can produce an extracellular 105–115 kDa soluble NCAM fragment (NCAM-EC) and a smaller intracellular cytoplasmic fragment (NCAM-IC). NCAM also undergoes a unique post-translational modification in brain by the addition of polysialic acid (PSA)-NCAM. Interestingly, both PSA-NCAM and NCAM-EC have been implicated in the pathophysiology of schizophrenia. The developmental expression patterns of the main NCAM isoforms and PSA-NCAM have been described in rodent brain, but no studies have examined NCAM expression across human cortical development. Western blotting was used to quantify NCAM in human postmortem prefrontal cortex in 42 individuals ranging in age from mid-gestation to early adulthood. Each NCAM isoform (NCAM-180, -140, and -120), post-translational modification (PSA-NCAM) and cleavage fragment (NCAM-EC and NCAM-IC) demonstrated developmental regulation in frontal cortex. NCAM-180, -140, and -120, as well as PSA-NCAM, and NCAM-IC all showed strong developmental regulation during fetal and early postnatal ages, consistent with their identified roles in axon growth and plasticity. NCAM-EC demonstrated a more gradual increase from the early postnatal period to reach a plateau by early adolescence, potentially implicating involvement in later developmental processes. In summary, this study implicates the major NCAM isoforms, PSA- NCAM and proteolytically cleaved NCAM in pre- and postnatal development of the human prefrontal cortex. These data provide new insights on human cortical development and also provide a basis for how altered NCAM signaling during specific developmental intervals could affect synaptic connectivity and circuit formation, and thereby contribute to neurodevelopmental disorders